The present disclosure relates to an internal combustion engine configured so that oil returns from a space above the cylinder head to the oil pan through the inside of the cylinder head and the inside of the cylinder block.
A cylinder block of an internal combustion engine described in Japanese Laid-Open Patent Publication No. 2014-105579 includes two recesses arranged to be adjacent to each other in a cylinder arrangement direction. The cylinder arrangement direction is a direction in which the cylinders are arranged in the cylinder block. A first oil chamber and a second oil chamber are formed in the cylinder block by closing the recesses with the cylinder head. Into the first and second oil chambers, oil in a space above the head existing above the cylinder head flows through first and second communication passages provided in the cylinder head.
An oil passage connected to both the first oil chamber and the second oil chamber is provided in the cylinder block. The oil accumulated in each oil chamber is returned to the oil pan through the oil passage.
When the amount of oil flowing into the space above the head increases due to increase in the engine rotation speed or the engine load factor, and the like, the amount of oil flowing into the oil chamber through the first and second communication passages increases and the pressure inside the oil chamber increases. Furthermore, when the engine rotation speed or the engine load factor increases, the pressure in the crankcase of the internal combustion engine and in the oil pan may increase. In this case, the blow-by gas in the crankcase flows backward through the oil passage and flows into each oil chamber. As a result, not only oil but also gas such as blow-by gas accumulates in each oil chamber.
Furthermore, the width in the cylinder arrangement direction of the first oil chamber and the width in the cylinder arrangement direction of the second oil chamber may be different from each other depending on the number of cylinders provided in the cylinder block. In this case, the number of communication passages connected to the oil chamber of which the width in the cylinder arrangement direction is narrower may become smaller than the number of communication passages connected to the oil chamber of which the width in the cylinder arrangement direction is wider.
For example, assume that the number of first communication passages connected to the first oil chamber is plural while the number of second communication passages connected to the second oil chamber is one. In this case, the resistance generated when causing gas to flow from the second oil chamber to the space above the head through the second communication passage is larger than the resistance generated when causing gas to flow from the first oil chamber to the space above the head through the first communication passage. As a result, compared with the discharge performance of the gas from the first oil chamber to the space above the head through each first communication passage, the discharge performance of the gas from the second oil chamber to the space above the head through the second communication passage becomes low. That is, gas tends to easily accumulate in the second oil chamber. In a state where the gas is accumulated in the second oil chamber, the oil is less likely to flow from the space above the head to the second oil chamber through the second communication passage. As a result, the amount of oil returning into the oil pan through the second oil chamber decreases, and the retained amount of oil in the oil pan decreases.
Therefore, there is room for improvement in suppressing hindrance of the circulation of the oil through the second oil chamber by the gas flowing into the second oil chamber.